Update docblocks

Author: jenssegers

src/Jenssegers/Mongodb/Relations/BelongsTo.php

@@ -40,6 +40,8 @@ public function getRelationExistenceQuery(Builder $query, Builder $parentQuery,
 
     /**
      * Get the owner key with backwards compatible support.
+     *
+     * @return string
      */
     public function getOwnerKey()
     {

src/Jenssegers/Mongodb/Relations/MorphTo.php

@@ -32,12 +32,12 @@ protected function getResultsByType($type)
     }
 
     /**
-     * get the Other/Owner Key name based on different version of Illuminate/Database
-     * see commit https://github.com/illuminate/database/commit/6a35698d72e276f435324b7e29b3cd37ef7d5d9c
+     * Get the owner key with backwards compatible support.
+     *
      * @return string
      */
     public function getOwnerKey()
     {
-        return property_exists($this, "ownerKey") ? $this->ownerKey : $this->otherKey;
+        return property_exists($this, 'ownerKey') ? $this->ownerKey : $this->otherKey;
     }
 }